MOTM

--- In motm@yahoogroups.com, Mark <yahoogroups@p...> wrote:
> 
> The output of an MOTM 800 is not an AC signal.  It is a positive 
> voltage that never crosses zero.  AC stands for "alternating
> current" -- it "pushes" current one way when the voltage is
> positive, and "draws" current the other way when its voltage is
> negative.

An EG could be classified as a DC source or an AC source depending 
upon which part of the envelope cycle is active.  In the "off" state 
(at zero) and in the sustain state the EG outputs a constant DC 
voltage.  In the attack, decay, and release state the EG outputs a 
time varying voltage which is essentially an AC waveform.

A signal does not need to "cross zero" to be considered AC.  For 
example, you could take a sine wave (AC) that is 2 volts peak to peak 
and add a 1 volt DC offset.  You still have a sine wave (AC) but 
instead of going from -1 volts to +1 volts, you now have a waveform 
that goes from 0 volts to 2 volts.  (It is still AC but it never 
crosses zero.)

Using that same example, we can think about AC coupled and DC coupled 
inputs.

If an input is AC coupled, it rejects DC offset.  If we feed our 
"normal" -1 to +1 sine wave into an AC coupled input, there is 
essentially no change in the waveform.  (It remains a -1 to +1 sine 
wave.)  On the other hand, if we feed our 0 to +2 sine wave into an AC 
couple input, the DC offset of 1 volt is eliminated by the AC coupling 
and what results is a "normal" -1 to +1 sine wave.

For DC coupled inputs, any DC offset remains in the signal.